1. Field of the Invention
The present invention relates to wireline units, and more particularly to apparatus for improving the safety and reliability of wireline units.
2. General Background of the Invention
In drilling of oil and gas wells, a wireline is often used to perform tasks such as perforating a casing and setting a gravel pack. Wireline is also used for other tasks, such as logging a well.
With use, wireline wears out and needs to be replaced, or it can break, causing whatever tool is at its lower end to fall into the well bore, along with whatever wireline is below the break. The downtime while the broken wireline and tool are being retrieved can cost an oil company thousands or even millions of dollars. Also, wireline is usually run through a blow-out-preventer (b.o.p.) valve. If there is a problem downhole (e.g., well pressure exceeding mud weight) and a blow out is imminent, the wireline is quickly retrieved and the b.o.p. valve is quickly shut. If the operator of the b.o.p. valve is nervous, he might shut the b.o.p. valve before the lower end of the wireline is above it, causing the wireline to break or possibly preventing the b.o.p. valve from closing.
Currently the use of wireline is counted by hand, as is the amount of wireline downhole. Inaccurate counting can lead to unexpected breaking of the wireline through the wireline wearing out. Also, mistakes in counting the amount of wireline downhole can cause the b.o.p. valve to be closed prematurely, damaging the valve and/or cutting the wireline. Further, if the location of the lower end of the wireline is not properly kept track of, a wireline tool attached to the lower end of the wireline may be pulled off of the wireline if the lower end of the wireline is pulled upward through an obstruction through which the tool cannot pass.